2.3. Experimental design and drying procedures
To compare the drying characteristics of IR and hot air drying, banana slices were dried at three IR intensities, 3000, 4000, and 5000 W/m2 and hot air at 62.8 °C. The weight changes were measured every minute using a digital balance during the drying. The 3000 W/m2 IR intensity had lowest drying rate among the tested intensities. The 5000 W/m2 IR intensity had the highest drying rate, but it caused discoloration of finished products at high weight reduction levels. Therefore, only 4000 W/m2 was then selected for producing predehydrated samples for freeze-drying. Both dipped and undipped samples were dried using IR to remove 20% and 40% of the initial weight. The weight reduction levels were determined for reasonably maintaining the texture integrity without causing too much shrinkage after IR drying. The predehydrated samples and a control sample without predehydration were further dried using freeze-drying to a final moisture content of about 5 g moisture/100 g wet weight for quality evaluation. The evaluated quality parameters included color, thickness shrinkage and crispness. All drying experiments were conducted in triplicate and the data reported in Section 3 are average values.